Im not sure about this but does Intel have a version of AMD's Cool N' Queit? It could be that, if your processor isnt under load it will slow down to save energy and keep it cooler. Not sure if intels have this or not.
EDIT: I just noticed you are using a laptop so thats probably it.

well cool n' quiet shouldn't decrease your speed that much if any at all, from what i've seen it just slows down your fan and gives less voltage at times, i may be wrong. also yes having a laptop windows will often underclock your processor to save power. so check ur power settings if u always want it running at full. also i have cool n' quiet on my intel. it slows down the fan speed and thats mostly it that i can see, it's an option on my asus motherboard.